1. Field of the Invention
The present invention relates to a thin-film magnetic head for magnetic recording including an electromagnetic coil element having magnetic layers, a head gimbal assembly (HGA) including the thin-film magnetic head, and a magnetic disk drive apparatus including the HGA.
2. Description of the Related Art
With the increasing demand for small, and yet high-capacity magnetic disk drive apparatus in recent years, further improvements in recording density have become essential. Important factors for increasing recording density include a reduction in the width along the track-width direction of the magnetic pole of the electromagnetic coil element in thin-film magnetic heads and an improvement of the intensity of the write field generated from the magnetic pole.
The electromagnetic coil element of a typical thin-film magnetic head has a lower magnetic layer (a magnetic layer on the leading side) and an upper magnetic layer (a magnetic layer on the trailing side) that sandwich a gap layer. The lower magnetic layer includes a rectangular projected portion having the same width along the track-width direction as that of the magnetic pole of the upper magnetic layer and a considerably wide portion below the rectangular projected portion, thereby efficiently guiding a magnetic flux excited by a write current flowing through the coil layer of the electromagnetic coil element to the gap layer and trying to cope with narrower track widths.
Structures of the lower magnetic layer are disclosed in U.S. Pat. No. 6,504,686 and Japanese Patent Publication 2000-315302A in which a non-magnetic layer is provided in a considerably wide portion of the lower magnetic layer. In these structures, the lower magnetic layer also acts as an upper shield layer for a magnetoresistive (MR) effect element for reading data provided adjacent to the electromagnetic coil element. In U.S. Pat. No. 6,504,686 and Japanese Patent Publication 2000-315302A, the non-magnetic layer formed in the structures alleviates adverse influences of the magnetic field from the electromagnetic coil element on the output characteristics of the MR effect element.
However, there has been a problem that the influence of a leakage magnetic field from the magnetic pole increases as the width of the magnetic pole along the track-width direction is reduced, and, as a result, increased is the probability of an unwanted write or erasure in adjacent tracks, namely Adjacent Track Erase (ATE), on a magnetic disk as a magnetic recording medium.
Especially in tracks near the outer edge of a magnetic disk and tracks near the center, the skew angle, i.e. an angle of the head with respect to the tracks increases and accordingly the magnetic pole on the leading side becomes closer to the adjacent tracks. As a result, increased is the possibility that a leakage magnetic field from the magnetic pole on the leading side causes ATE. To prevent this, the saturation magnetic flux density of the magnetic pole on the leading side may be reduced to reduce the leakage magnetic field. However, this limitation inevitably reduces the intensity of the write field itself.
Another solution to suppress ATE may be to increase the neck-depth of the lower magnetic layer. The term neck-depth herein refers to the length of a rectangular projected portion of a lower magnetic layer along the stacking direction. The neck-depth in practice is an amount that is adjusted during formation of the rectangular projected portion by ion etching using a magnetic pole portion of an upper magnetic layer as a mask. However, the neck depth cannot be increased above a certain value simply by increasing the amount of etching with the current state of the art, because this increase has disadvantageous effects such as shortening of the magnetic pole portion of the upper magnetic layer, increase in unevenness of a magnetic pole width, and impairment of controllability of the magnetic pole width.
The lower magnetic layer including a non-magnetic portion disclosed in U.S. Pat. No. 6,504,686 and Japanese Patent Publication 2000-315302A only adds the magnetic shield effect between the MR effect element and the electromagnetic coil element, and cannot reduce a leakage field from the magnetic pole on the leading side.